Many aspects of the food web in the sea are ill understood: none more than the quantitative aspects of the heterotrophic activity of micro-organisms. Heterotrophic utilization of dissolved organic material by micro-organisms was recognized and discussed in principle by such workers as ZoBell, Waksman and Rakestraw in the thirties. There has been very little subsequent progress in understanding the details of the process, principally because of the lack of a suitable approach. Parsons and Strickland (1961) revived interest in this field when they introduced a simple radiochemical technique to follow the uptake of individual soluble organic compounds; subsequently Williams & Askew (1968) developed a method to measure the respiration of such compounds in sea-water samples.

In the sea, heterotrophic bacteria and other micro-organisms oxidize dissolved organic material. This process is important to the seasonal biological cycle of matter there because it is responsible for the return of an appreciable fraction of the inorganic nutrients (Andrews & Williams, 1971). It is also important in the process whereby the sea purifies itself of added dissolved organic pollutants: domestic and industrial wastes and spillages. These two processes, especially the latter, pose important and unanswered questions. One in particular is the behaviour of these heterotrophic populations when subjected to sudden increases in the concentration of an organic substrate. This will occur to some degree under natural conditions in sea water during or after a phytoplankton bloom and will occur to a considerable degree when pollutants are run into the sea.

In 1959 and 1960 eight surveys were made in an area about 54 x 83 km in the English Channel immediately south of Plymouth (Armstrong & Butler, 1962b). Measurements of temperature and salinity and of phosphate and silicate concentrations showed a good deal of variation from place to place so that it would be difficult to accept results from any one station as typical of the area. The density distributions suggested a general eastward movement in the winter and, in summer, a movement of surface water offshore from the English coast, with a corresponding onshore movement of deeper water.

The degree of exposure of a beach to wave action largely determines particle size, sorting and beach gradient (King, 1959) and these, in turn, have a dominant effect on the animal communities within the sand (Swedmark, 1964; Mclntyre, 1969). It is likely, however, that the main turnover of energy, as indicated by the rapid removal of oxygen (Brafield, 1964; Hamilton & Greenfield, 1967), is due to bacteria and algae. On sheltered muddy beaches, motile diatoms can be of considerable importance (Aleem, 1950; Perkins, 1960) but for a relatively exposed beach at Firemore, Loch Ewe, on the west coast of Scotland, Fig. 1, there was negligible unattached plant material, living or dead, and the primary production by the diatoms attached to the sand grains was low (Steele & Baird, 1968). Further, these diatoms did not show evidence of heterotrophy (Munro & Brock, 1968; Mclntyre, Munro & Steele, 1970) yet, at low water mark on this beach, the populations of attached diatoms are relatively uniform to a depth of 20–30 cm in the sand and show no sign of pigment degradation or decreased photosynthetic ability. These conditions at low water mark differ from those at a water depth of 5–10 m where chlorophyll concentration in the upper 5 cm of the sand is higher but where pigment degradation and blackening of the sand, indicating reducing conditions, are usually found below 10 cm depth of sand.

Oil pollution in marine waters has been a subject of growing concern and has stimulated a variety of pollution studies. Past methods of dealing with the problem have been mechanical, which are effective on land, and chemical which, in the past, have used highly toxic detergents, usually in open waters (Spooner, 1969).

The fouling of formerly clean sandy shores by the weathered residues of crude oil is all too familiar. Vigorous use of solvent emulsifiers can restore the beach ‘whiter than white’ but this damages the creatures which normally live in and on the sand. Unless the oil pollution is continual, the beach will usually rid itself of oil aided by waves and tides. Sometimes the disappearance of the oil may amount to no more than its bodily removal elsewhere or its burial out of sight, but inevitably, its ultimate destruction must be as the result of photochemical and biological processes. For intertidal sands where oil may become buried by wave action, the photochemical aspect is perhaps less important than for floating oil and the biological pathway is more important. In the experiments described here an attempt is made to investigate the rate of oil destruction by natural beach micro-organisms. Under the experimental conditions used, it is not difficult to sustain over a period of several months a fairly representative model of a beach with its populations of bacteria, diatoms and interstitial benthic animals.

This study forms a contribution to a series (Angel, 1969; Clarke, 1969; Baker, 1970; Badcock, 1970) describing the biological results of a detailed investigation of the ecology of an oceanic area located in the eastern North Atlantic, close to the island of Fuerteventura (Canary Islands). The scientific background and objectives of the investigation, conducted during September to December 1965, have been described elsewhere (Currie, Boden & Kampa, 1969). Our main interest lay in the biological composition and acoustic characteristics of sonic scattering layers, and it was therefore considered essential to sample the principal elements of the pelagic fauna within the depth range 0–1000 m in as quantitative and detailed a manner as was technically possible. The resulting biological collections represent a unique body of material, the analysis of which is directly pertinent to the vertical distribution, diurnal migration and ecological interrelationships of the mesopelagic fauna.

This paper represents the second and final part of a study of the depth distribution and diurnal migration of pelagic decapod crustaceans in an area of the eastern North Atlantic. Part I (Foxton, 1970) dealt with the Caridea; Part II now considers the Penaeidea. In the discussion the data as a whole are analysed and the resulting patterns of vertical distribution and migration discussed.

The features of the vertical distribution of meso- and bathypelagic fishes are poorly known. Much of our present knowledge is based upon data collected on the early, major expeditions (i.e. Brauer, 1906; Murray & Hjort, 1912; Jespersen, 1915; Jespersen & Tåning, 1926; Norman, 1929, 1930; Regan & Trewavas, 1929, 1930; Benin, 1934, 1937; Ege 1934 1948, 1953, 1957; Bertelsen, 1951; Parr, 1960; Ebeling, 1962; Ebeling & Weed, 1963; Nafpaktitis, 1968). Fishing depths were not accurately determined, the depth of net generally being calculated from the length of wire out and the wire angle to the water surface. Closing nets were infrequently used. From these reports a general appreciation of vertical distributions has been possible. More recently, distribution studies mostly made in restricted areas using open nets with depths more accurately determined indicate a limited vertical distribution for each species (Aron, 1962; Pearcy, 1964; Pearcy & Laurs, 1966; Lavenberg & Ebeling, 1967; Paxton, 1967).

Some years ago it was shown that adult limpets, Patella vulgata (L.), could give a graded response to water of diminished salinity, the precise extent of which varied according to the tide level from which the individual was drawn (Arnold, 1957). This response, an upward movement of the front edge of the shell, accompanied by protrusion of the cephalic and mantle tentacles, was elicited by dilutions of sea water with a salinity as low as 17‰ in the case of limpets living near H.W.N.T., but was not shown to salinities below about 27‰ by those settled near L.W.S.T. Such a difference in tolerances and behaviour could be expected to play an important part in the lives of intertidal organisms, especially those of a sessile or sedentary habit, since it would permit populations inhabiting the higher levels of the shore to maintain activity despite the generally disadvantageous nature of prolonged exposure to the air. Moreover, those species capable of such adaptations might, under estuarine conditions, evolve physiologically different populations specially fitted for life under conditions of low salinity. Such studies are thus of value not only in regard to the biology of the particular species concerned, but also for fuller understanding of the general conditions of intertidal and estuarine life and their practicability as routes toward establishment of a terrestrial mode of life. Subsequent studies have revealed the salinity tolerances of a number of intertidal organisms, including those of the larvae of both the commoner barnacles and several families of polychaetes (Bhatnagar & Crisp, 1965; Lyster, 1965). Investigation with media of various compositions suggests that in both limpets and barnacles the response is essentially to the presence of chloride ion, modulated by the presence of calcium ion (Arnold, 1959; Barnes & Barnes, 1958).

Several authors have studied the rhythmic behaviour of amphipods, including Papi (1955) who demonstrated an endogenous solar time sense in Talitrus saltator which was used for navigation. Talitrids were also investigated by Featherston & Maclntyre (1957) who suggested that changes in light intensity triggered the nocturnal foraging activity. Enright (1961, 1962, 1963) tested the effects of pressure, temperature, light intensity, absence of sand and shaking on rhythmic behaviour of the intertidal and in-faunal amphipod Synchelidium. The activity rhythm of Corophium volutator has been reported by Morgan (1965) in which a peak occurred on the early ebb. Various rocky shore Peracarida including species of Gammarus also perform vertical migrations into the surf at night (Jansson & Källander, 1968); the inhibiting effect of light was proven by experiments with controlled illumination.

When littoral animals are exposed by the receding tide they are subjected to the environmental factors of what is essentially a terrestrial environment. Of these factors desiccation (see Davies, 1969) and temperature are of paramount importance. In winter the animals may be subject to a rapid change from the relatively high temperature of the sea to a very much lower air temperature. In summertime the opposite is true and the animals will spend the dry phase in air temperatures often far in excess of sea-water temperatures. The most important temperatures from an ecological point of view, however, are the body temperatures of the animals themselves. As shown by Southward (1958) this cannot be deduced from measurements of air temperatures, since the animals are subject to heating by absorption of solar radiant energy and this in turn may be mitigated by other environmental factors.

Marinogammarus obtusatus Dahl, an intertidal amphipod, was first described by Dahl (1938). Prior to this date it appears that this species was often confused with and identified as M. marinus. In later years, M. obtusatus has been shown to be common around the coast of Britain (Sexton & Spooner, 1940), and in a preliminary survey of Cullercoats Bay, Northumberland, we have found that this species is by far the commonest amphipod present.

The common dog-whelk, Nucella (= Thais, = Purpura) lapillus (L.), is often selected for ecological, physiological and genetical study. In recent years most workers have based their investigations on the work of Moore (1936; 1938a, b) and most have used his observation that ‘at the onset of maturity, growth of the (shell) lip ceases and instead the region near the lip thickens, while the lip itself becomes rounded and a series of rounded “teeth” develop on its inner side which still further occlude the opening’. It has been assumed that all animals showing these features are adult, and have ceased growing, for Moore goes on to say ‘occasional specimens are taken in which the presence of a second set of teeth within the marginal ones indicates that the original stoppage of growth was followed by a second slight growing period, this in turn being replaced by a second period of thickening and growth stoppage, but such specimens are too rare to be a serious source of error.’ This assumption has been incorporated into most subsequent reviews of shore ecology.

When first described, as the type species of a new genus (Butcher, 1952), Pavlova gyrans was thought to be separable from Ochromonas by only one major character, namely the lateral instead of the supposedly terminal insertion of the strongly anisokont flagella. It was therefore natural to include it in the class Chrysophyceae and to interpret other structural features in accordance with this view. This practice has been continued to some extent subsequently and the three named species which are now recorded in the literature are all in varying degrees in need of emended descriptions. For this particular genus is deceptive. Not only are there unusual fixation difficulties, as already noted by Butcher, but even when examined alive its appearance can suggest the presence of characters which are not in fact what they seem to be and mask others which are essential for taxonomic guidance. Even when all these difficulties have been overcome, certain details are so unusual as to be without known parallel among the ‘brown’ flagellates which have so far been studied with the electron microscope.